There has been proposed two-dimensional communication in which communication and power supply are carried out using a sheet-shaped antenna. In this sheet-shaped antenna, for example, two sheet conductor portions are arranged so as to face each other and dielectric is filled therebetween as with the signal transmission systems disclosed in Patent Documents 1 and 2. A portion of one of the sheet conductor portions except the edge thereof forms a grid composed of a conductor. By connecting a dedicated coupler for transmitting and receiving electromagnetic waves, communication and electric power supply are realized. The characteristics of electromagnetic waves that propagate through the sheet conductor portion are characterized by the sheet impedance.